Process and device for the coating of substrates by means of bipolar pulsed magnetron sputtering and the use thereof

ABSTRACT

Process and device for coating substrates utilizing bipolar pulsed magnetron sputtering in the frequency range between 10 and 100 kHz, wherein the device includes at least three magnetron sources. Each of the at least three magnetron sources includes a target. At least two of the targets are connected to a potential-free bipolar power supply device. The at least three targets are arranged relative to the substrates in such a way that the substrates are located at least partially inside a discharge current during a coating of the substrates. A switching device is adapted to connect the targets to the bipolar power supply device. A technological predetermined program is used for controlling the switching device. The switching device connects at least two of the targets at a time to the bipolar power supply device according to the technologically predetermined program.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage Application of InternationalApplication No. PCT/DE99/04132, filed Dec. 27, 1999. Further, thepresent application claims priority under 35 U.S.C. §119 of GermanPatent Application No. 198 60 474.2 filed on Dec. 28, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process and a device for the coating ofsubstrates by way of bipolar pulsed magnetron sputtering in thefrequency range of 10 kHz to 100 kHz. The invention is particularlyintended to deposit layers with poor electrical conductivity orinsulating layers onto substrates. Such layers are preferably used asoptical, electrical, or mechanical functional layers as are needed foroptical components, electrical components, or for friction-reducing andwear-retarding protective layers.

2. Discussion of Background Information

Magnetron sputtering is widely used for depositing metallic andelectrically insulating layers. The recent introduction of reactivepulsed magnetron sputtering brought about significant progress,especially for the economical deposition of layers with poor electricalconductivity or insulating layers (Schiller et al., Society of VacuumCoaters, 38th Annual Technical Conference Proceedings 1995, pages293-297).

Processes for unipolar and bipolar pulsed magnetron sputtering areknown. In unipolar pulsed magnetron sputtering, the energy is fed intothe target in the form of direct current pulses. A special manner offeeding unipolar pulsed energy using several targets sputtered in aunipolar fashion is described in DE 197 02 187. Here, at least one oftwo magnetron electrodes is connected cathodically and at least one isconnected anodically and the discharge energy is fed in a unipolarfashion during a defined period of time with a pulse frequency of 10 to150 kHz. Then the power supply is interrupted and a polarity reversal isperformed.

Particularly high process stability and the possibility of coating largeareas of largely uniform surfaces can be achieved by means of reactivesputtering with a double magnetron arrangement using a bipolar pulsedpower supply with a frequency for the polarity change of 10 kHz to 100kHz. Here, it is less significant for the process whether a clockeddirect current source or a medium frequency generator is selected as thetype of pulsed power source.

In a double magnetron arrangement that has been introduced in the fieldof coating technology as a dual magnetron system or TwinMag (Bräuer etal., Proc. of the 3rd ISSP, Tokyo 1995, pages 63-70), each target of thedouble magnetron arrangement acts alternately as a cathode or an anodeof a gas discharge burning between the targets in the rhythm of thepolarity reversal. Known arrangements consist of two magnetron sourcesarranged parallel to one another with rectangular targets that lie in aplane or are inclined toward one another at a particular angle in theshape of a roof. The overlapping of the magnetic fields of the twomagnetron sources occurring here requires special measures or devicesfor compensating for the uneven erosion speed of the various regions ofthe target. In general, however, despite these measures, target erosionoccurs with greater speed in the region of the closely adjacent erosionchannels than in the region of erosion channels that are more widelyseparated from one another. This leads to a shortening of the usefullife of the cost-intensive target.

A deciding factor for the quality of the layers deposited by-means ofsputtering is the plasma density, i.e., the density of charged particlesin the region of the substrates. It influences the average energy of thecondensing particles and thus the structure of the layers and many otherphysical layer characteristics. In the region near the target, theplasma density is very high during magnetron sputtering. However, itdecreases very quickly in the direction of the substrates and is less byorders of magnitude in the region of the substrate.

Various processes and/or devices are known from coating technology withsingle magnetron sources that have the purpose of increasing the plasmadensity in the region of the substrates. Thus, the spatial plasmadensity is changed by means of asymmetrical formation of the magneticfield of the magnetron source in such a way that the plasma density isincreased in the region of the substrates (Window and Savvides,Unbalanced DC Magnetrons as Sources . . . , J.Vac.Sci.Technol. A4 (3)1986, pages 453-456).

Similar effects are achieved with magnetic fields that are produced bymeans of additional coils, or so-called plasma booster arrangements(Hofmann, New Multilayer PVD Coating Techniques for Cutting Tools,Surf.Coat.Technol., No. 61 (1993), pages 326-330). Arrangements withfour direct current magnetron sources are also known whose magneticfield poles are arranged such that their overlapping achieves a closedmagnetic field with increased plasma density in the vicinity of thesubstrate.

In pulsed magnetron sputtering with double magnetron arrangements, theregion of higher plasma density is located near the surface of thetargets, in particular also in the vicinity of the gap between thetargets. The layers deposited on the substrates condense under theinfluence of a comparatively low plasma density and therefore havequality defects in many cases. There is no known adaptation of themethods or arrangements for displacing the region of high plasma densityin the direction of the substrate to double magnetron arrangements. Ofthese measures, only the introduction of large-area additional coilswould be conceivable to one skilled in the art. However, a higherequipment expense and only limited effectiveness could be expected.

The concentration of the plasma in the immediate vicinity of the doublemagnetron arrangement has a particularly disadvantageous effect whenthree-dimensional extended substrates or substrates that are arranged onmovable holders such as rotating cages or rotating substrate receptacleswith several parallel rotational axes for the purpose of even coverageare to be coated in the immediate vicinity of the double magnetronarrangement. According to the prior art, the condensation of the layerson such substrates during pulsed magnetron sputtering occurs with aplasma density that differs greatly locally and, in the case of movablesubstrates, with a plasma density that differs over time. Seriousdisadvantages in terms of layer structure and local uniformity of layercharacteristics result from this.

SUMMARY OF THE INVENTION

The invention provides for a process and a device for coating ofsubstrates by way of bipolar pulsed magnetron sputtering that guaranteeshigh-quality deposition of the layers. In particular, substrates thatare extended in three dimensions and/or substrates and groups ofsubstrates in the form of substrate arrangements that are arrangedduring coating on holders, preferably movable holders, such as rotatingcages or rotating substrate receptacles with several parallel rotationalaxes, should also be coated at high quality. Moreover, the inventionalso provides for applications for the process and the device accordingto the invention.

The invention provides for a process for coating substrates utilizingbipolar pulsed magnetron sputtering in the frequency range between 10kHz and 100 kHz in a device which includes at least three targets, theprocess comprises connecting at least two targets at a time to apotential-free bipolar power supply device, sputtering the at least twotargets in a bipolar manner for a predetermined period of time, changingthe connecting of the at least two targets to the bipolar power supplydevice according to a technologically predetermined program, andarranging the at least two targets relative to the substrate in a mannersuch that during each of a reversing discharge, the substrates beinglocated at least partially inside a discharge current between thetargets which are active at the time.

The changing may occur one of temporally periodically and aperiodically.The predetermined period of time may comprise at least 10 polarityreversals of a bipolar magnetron discharge. The predetermined period oftime may comprise between 1,000 and 100,000 polarity reversals. At leastone of a material of the targets and the technologically predeterminedprogram may be adapted to a desired layer deposition. At least one of amaterial of the targets and the technologically predetermined programmay be adapted to a desired coating task. The substrates may comprise atleast one of an optical, an electrical, and mechanical component ortool.

The invention also provides for a device for coating substratesutilizing bipolar pulsed magnetron sputtering in the frequency rangebetween 10 and 100 kHz. The device comprises at least three magnetronsources. Each of the at least three magnetron sources comprises atarget. At least two of the targets are connected to a potential-freebipolar power supply device. The at least three targets are arrangedrelative to the substrates in such a way that the substrates are locatedat least partially inside a discharge current during a coating of thesubstrates. A switching device is adapted to connect the targets to thebipolar power supply device. A technological predetermined program isused for controlling the switching device. The switching device connectsat least two of the targets at a time to the bipolar power supply deviceaccording to the technologically predetermined program.

The at least three targets may comprise at least four targets. At leasttwo of the at least four targets may be arranged on one side of thesubstrates and wherein at least two of the at least four targets arearranged on another side of the substrates. The at least three targetsmay be arranged to surround the substrates. At least one of the at leastthree targets and the substrates may be adapted to be movable. The atleast three targets may comprise four targets, wherein two of the fourare arranged on opposite sides of the substrates, and one of the twotargets on each side of the substrates may be adapted to besimultaneously connected to the bipolar power supply device. At leastone of the at least three targets may be connected to the bipolar powersupply device and at least two of the at least three targets may beconnected to the switching device. At least one of the at least threetargets may comprise a central target which is centrally disposed and atleast two of the at least three targets may comprise peripheral targetswhich are peripherally arranged, whereby the substrates are disposedbetween the central target and the peripheral targets. The centraltarget may be at least one of tube-shaped, connected to the bipolarpower supply device, and a centrally rotatable magnet arrangement. Thecentral target may be rotatable. The at least three magnetron sourcesmay be spaced apart such that their corresponding magnetic fields do notsignificantly influence one another. The device may further comprise adevice arranged to surround the at least three magnetrons. The devicearranged to surround the at least three magnetrons may comprise one of agrounded screen and potential-free screen. The device arranged tosurround the at least three magnetrons may protrude into an open areabetween a target plane and the substrates. The substrates may compriseat least one of an optical, an electrical, and mechanical component ortool.

The invention also provides for a device for coating substratesutilizing bipolar pulsed magnetron sputtering in the frequency rangebetween 10 and 100 kHz. The device comprises a bipolar power supply. Aswitching device is coupled to the bipolar power supply. A program isadapted to control the switching device. At least three magnetronsources are included. At least two of the at least three magnetronsources is coupled to the switching device. At least one of the at leastthree magnetron sources are coupled to one of the switching device andthe bipolar power supply. Each of the at least three magnetron sourcescomprises a target. The switching device connects at least two of thetargets at a time to the bipolar power supply according to the program.

According to the invention three or more targets are arranged relativeto the substrates in such a way that the substrates are locatedessentially in the region of high plasma density when at least two ofthe targets are respectively connected to the target terminals of abipolar power supply device and, in the course of the coating process,the specific targets connected to the power supply device are changedaccording to a technologically predetermined program.

Here, it has been shown that bipolar pulsed magnetron sputtering in thefrequency range between 10 kHz and 100 kHz can also be operated in astable manner with magnetron sources that are arranged at a largespatial distance from one another. In this operating mode, the plasma isextended to a large-area region between the magnetron sources and alsohas a high density in the region of the substrates arranged there. Ifthe sputtering process is performed with more than two magnetron sourcesand the selection and switching time of the targets connected to theterminals of the power supply device is controlled by way of anappropriate program, then an appropriate, preferably uniform,distribution of the plasma density in the entire three-dimensional spacecontaining the substrates can be achieved averaged over time.Advantageously, the program can be structured in such a way that, at thesame time, several targets are connected to the positive pole andseveral other targets are connected to the negative pole. Compared tobipolar pulsed magnetron sputtering using a double magnetron arrangementaccording to the prior art, layers can be deposited on the substrates inthis manner with higher plasma activation. They have an improvedstructure, for example, a higher density, greater crystallinity, and ahigher isotropy of crystal growth. This results in advantageous optical,electrical, and mechanical characteristics of the layers.

Depending on the technological needs, it can also be useful for theprogram for switching the targets connected to the power supply deviceto be set in a temporally aperiodic manner. One example of this is thedeposition of layer systems by way of bipolar pulsed magnetronsputtering when these systems include several partial layers, of whichat least two contain one and the same metallic component. In thismanner, the equipment expense can be reduced by reducing the totalnumber of targets required. However, even more crucial is the increasein layer quality that results from the further increase in plasmathickness as a result of the spatial concentration.

Furthermore, it can be useful for the program to contain temporallyperiodic switching. This process is especially appropriate for thedeposition of layers on substrate arrangements that are extended oververy large areas. If, for example, the connection of two given targetswith the bipolar power supply device is maintained only for a period oftime in which the position of the substrates changes onlyinsignificantly, then a maximal homogenization of the plasma densityresults.

A particular advantage of the process lies in the fact that thedischarge voltage of the bipolar magnetron discharge according to theinvention as compared to the discharge voltage of a double magnetronarrangement according to the prior art under comparable conditions ofthe target material, gas composition, and gas pressure at the sameenergy supply can be substantially increased by increasing the impedanceof the gas discharge. The increase can lie between 5 and 25%. Thus, ahigher average energy of the particles and a further increase in plasmaactivation in layer condensation is achieved.

If one layer, preferably of a metal compound that has poor electricalconductivity or is insulating, is to be deposited, then the process isperformed using at least three magnetron sources with targets made ofthe same metal.

During deposition of a layer system composed of partial layers in whichat least one metallic component is the same, magnetron sources are usedwith targets of different materials. Here, the program for switching isstructured in such a way that, in addition to homogenization of theplasma distribution, the desired composition and thickness of thepartial layers is ensured.

If the extension of the substrates is considerably lower in onedimension than in the other two dimensions, it is useful to arrange thetargets of the magnetron source in two levels, with the substrates beinglocated between the targets and at least two targets located across fromone another being sputtered in a bipolar manner.

For the coating of other substrates, in particular when they are to becoated on all sides and are moved for this purpose, a device is usefulin which at least two of the magnetron sources are across from oneanother. A particularly useful device contains at least three magnetronsources that are arranged in a circle around the substrates atapproximately the same angular distance from one another. The angle abetween the target normals then amounts to 360°/k, where k is the numberof magnetron sources.

Usefully, one device includes magnetron sources whose targets aresurrounded by a grounded or potential-free screen that extends into theopen space between the target plane and the substrates. With the aid ofsuch screens, the impedance of the gas discharge is increased, anincrease of the average energy of the condensed particles is achieved,and the plasma density in the region of the substrate is increased

It is useful for the device to be structured in such a way that such alarge distance between the individual magnetron sources results andtheir magnetic fields do not substantially influence one another. Thischaracteristic in connection with an appropriate switching programensures a largely uniform sputtering of the target on all regions of theerosion channels and thus a long service life of the target.

By way of a suitable structure of the switching program, it can beachieved that, on the average, each target is connected to other targetsfor an equal length of time and thus all targets are essentially evenlysputtered.

Another useful device with substrates arranged in the shape of a ringcontains magnetron sources that are arranged around the substrates in acircle and whose target normals point in the direction of the substrate.The arrangement can furthermore have one or more magnetron sourcespositioned in the center of the substrate arrangement, whose targetnormals also point in the direction of the substrate. By way of theswitching program, it is ensured that, at least for portions of thecoating time, one or more outer magnetron sources and one or more innermagnetron sources at the same time are acting together with the pulsedpower supply device.

The device mentioned above can also advantageously be modified such thata magnetron source having a tube-shaped target and a magnet arrangementthat may be rotated around the axis of symmetry of the target tube ispositioned in the center of the substrate arrangement. The magnetarrangement is then aligned with the respective target, which isconnected to the power supply device at the same time.

If substrates that are moved in a linear fashion are to be coated, itcan be useful to arrange several magnetron sources in two rows such thattheir target normals are pointed to the substrate. For this purpose, theswitching program is structured in such a way that, at least forportions of the coating time, one or more magnetron sources of the onerow are simultaneously working together with one or more magnetronsources of the other row.

In this description, substrate is to be understood fundamentally as theindividual substrate as well as the arrangement of several substrates inso-called substrate carriers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall be described in greater detail in the followingusing four exemplary embodiments.

FIG. 1 shows the principle of bipolar pulsed magnetron sputtering usinga double magnetron arrangement according to the prior art.

FIG. 2 shows a device according to the invention with three magnetronsources arranged peripherally to the substrates.

FIG. 3 shows a device according to the invention with four magnetronsources that are arranged in two planes on both sides of the substrates.

FIG. 4 shows a device with substrates arranged in the shape of a ring, acentral magnetron source, and six peripheral magnetron sources.

FIG. 5 shows a device for producing a system of several layers on atube-shaped substrate corresponding to the process according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, the principle of bipolar pulsed magnetron sputtering using adouble magnetron arrangement according to the prior art is shown for thepurpose of explanation. A double magnetron arrangement is used by way ofexample for coating the substrate 7. It contains two rectangular targets8 and 8′ with the associated magnet arrangements 9 and 9′. The targets 8and 8′ are arranged parallel to one another and separated from oneanother by a narrow gap 10. Normally, a double magnetron arrangement issurrounded by a common housing 11. The targets 8 and 8′ lie in oneplane.

Constructions are also known from the prior art in which the targetnormals form an angle α<180°. The targets 8 and 8′ are each connected toone of the output terminals 12 and 12′ of the potential-free bipolarpulsed power supply device 13. After the ignition of a glow discharge, aplasma 14 forms, which is essentially concentrated in the region nearthe target and in the region of the gap 10 between the targets 8 and 8′.In the program scheme 1 pertaining to the bipolar pulsed power supplydevice 13, the temporal progression of the bipolar pulsed energy isdepicted schematically. If, during the glow discharge and thus duringthe sputtering, the frequency for the polarity reversal is selected inthe preferred range of 10 kHz to 100 kHz, a high degree of processstability is achieved for the magnetron sputtering. This is also truefor the reactive deposition of electrically insulating layers. In otherfrequency ranges, the specific advantages of bipolar pulsed magnetronsputtering are lost.

The disadvantage of solutions according to the prior art lies in thefact that the core region of the plasma 14 forms on the short pathbetween the targets 8 and 8′ and it is difficult in practice to bringthe substrate close to this region in order to achieve an effectivedeposition of the material sputtered by the targets 8 and 8′ onto thesubstrates under the influence of a dense plasma.

FIGS. 2 to 5 show various exemplary embodiments using the devicesaccording to the invention.

Exemplary Embodiment I

FIG. 2 shows a vacuum coating chamber 16 in which the substrates 15 arecentrally arranged. Three magnetron sources 17, 17′, and 17″ with magnetarrangements and metallic targets 18, 18′, and 18″ are arrangedperipherally to the substrates 15. The normals of the targets 18, 18′,and 18″ are aligned evenly to the substrates 15 and to one another at anangle α of 120°. Each magnetron source 17, 17′, and 17″ is surrounded bya housing 19, 19′, and 19″, which achieves dark space yielding. Thetargets 18, 18′, and 18″ are electrically connected to a switchingdevice 20. A potential-free bipolar pulsed power supply device 21 servesthe purpose of energy supply.

An application of the device described above for coating of thesubstrate using the process according to the invention shall bedescribed in greater detail in the following.

The reactive bipolar pulse magnetron sputtering occurs using theswitching device 20 in such a way that, for certain time periods of thecoating process, two of the three magnetron sources 17, 17′, and 17″ arerespectively connected to the terminals of the pulsed power supplydevice and such that the selection of the magnetron sources 17, 17′, 17″and the duration of their joint action is controlled according to apredetermined program. During use, two neighboring magnetron sources 17,17′, and 17″ are respectively connected to the power supply device 21for the duration of one second. At a frequency of polarity reversal ofthe bipolar pulsed magnetron discharge of 50 Hz, this corresponds to50,000 polarity reversals. Another combination of two of the threemagnetron sources 17, 17′, and 17″ is then connected to the power supplydevice 21 for the duration of one second in turn, and so on. The programensures that each magnetron source 17, 17′, and 17″ is connected for anequal period when averaged over time. In the exemplary embodiment, incontrast to the use of double magnetron arrangements according to theprior art, the entire space surrounding the substrates 15 is filled witha dense plasma. If a bias is placed on the substrates, a high ioniccurrent (e.g., 10 to 100 mA/cm²) can be extracted. In the program scheme2, pertaining to the switching direction 20, the temporal progression ofthe bipolar pulsed current is shown schematically, which is provided bythe bipolar pulsed power supply device 21 for the individual magnetronsources 17, 17′, and 17″ with the targets 18, 18′, and 18″.

Exemplary Embodiment II

In FIG. 3, the invention is explained in detail using the example ofbipolar pulsed magnetron sputtering for coating a substrate that isextended in its area. The substrate 22, which is provided with openings,is moved in the direction of the arrow through the coating space betweenfour magnetron sources 24, 24′, 24″, and 24′″ for the purpose ofcoating.

A reactive bipolar pulsed magnetron discharge is to be performed by wayof example. For this purpose, the coating space is filled with anargon-nitrogen mixture. The material to be sputtered is provided in theform of four rectangular plates, which are provided as targets 23, 23′,23″, and 23′″ at the four magnetron sources 24, 24′, 24″, and 24′″.

The magnetron sources 24, 24′, 24″, and 24′″ are surrounded by housings25, 25′, 25″, and 25′″. The magnetron sources 24 and 24′ are arranged ina lower row and the magnetron sources 24″, and 24′″ are arranged in anupper row. All target normals are pointed at the substrates in aparallel and/or antiparallel manner. The targets 23, 23′, 23″, and 23′″are thus arranged on both sides of the substrates 22. A switching device26 connects two of the magnetron sources 24, 24′, 24″, and 24′″ at atime to the output terminals of a bipolar pulsed power supply device 27for a given duration.

In the program scheme 3, pertaining to the switching direction 26, thetemporal progression of the bipolar pulsed current is shownschematically, which is provided by the bipolar pulsed power supplydevice 27 for the individual magnetron sources 24, 24′, 24″, and 24′″with the targets 23, 23′, 23″, and 23″.

The program scheme 3 clarifies the program for the selection andswitching duration of each combination of the magnetron sources 24, 24′,24″, and 24′″. A schematically depicted time unit represents 0.1seconds, so that the program operates with a period duration IP of 1.2seconds. For the entire coating process this sequence is cycled through500 times, for example.

Exemplary Embodiment III

FIG. 4 shows a device with substrates 28 arranged in the shape of aring, a central magnetron source with a tube-shaped target 29, and arotatable magnet arrangement 30 in the interior of the target 29. Sixmagnetron sources 31 with targets 32 are arranged coaxially andperipherally to the substrates 28.

In the exemplary embodiment, the substrates 28 are located in holders byway of which they are rotated in a planetary manner around the centralaxis of the arrangement as a whole and around their own axes.

The magnetron arrangement 30 rotates uniformly with a rotational speedof 20 min⁻¹ about the central axis of the device. The normals of thetargets 32 are oriented toward the center. All outer magnetron sources31 have an angular distance of 60° from one another.

The power supply of the target 32 is accomplished by a bipolar pulsedpower supply device 34 by way of a switching unit 33. Here, for example,the switching unit 33 works with a program in which three neighboringmagnetron sources 31 are respectively switched in parallel and areconnected to an output terminal of the bipolar pulsed power supplydevice 34. The central magnetron source with the tube-shaped target 29is constantly connected to the other output terminal of the power supplydevice 34.

The program scheme of the switching unit 33 provides for each of thethree targets 32 to be connected in parallel manner and to be connectedto an output terminal of the power supply device 34 that faces theinstantaneous position of the magnet arrangement 30 of the centralmagnetron source. In this manner, a steam and plasma cloud is producedwhose greatest concentration circulates with the rotational speed of themagnet arrangement 30 of the central magnetron source.

Exemplary Embodiment IV

FIG. 5 illustrates a device for depositing a layer system consisting,for example, of three partial layers, using the process according to theinvention and a device according to the invention.

A tube 35 is to be provided on its outer side with a layer system thatincludes the partial layers titanium nitride (TiN), titanium aluminumnitride (TiAlN), and aluminum oxide (Al₂O₃). The tube 35 rotates aboutthe axis 36 during coating. The device utilizes two magnetron sources 37and 37′ with the titanium targets 38 and 38′ and two magnetron sources37″ and 37′″ with the aluminum targets 38″ and 38′″.

In a first process section, sputtering of the titanium targets 38 and38′ occurs in an argon-nitrogen mixture. By way of the switching device39, both of the output terminals of the bipolar pulsed power supplydevice 40 are connected to the titanium targets 38 and 38′. After thenecessary thickness of the titanium nitride layer deposited in thisprocess step has been reached, the titanium target 38 and the aluminumtarget 38″ and correspondingly the titanium target 38′ and the aluminumtarget 38′″ are respectively connected to the output terminals of thepower supply device 40 by the switching device 39 according to theprogram. Both target pairs are alternately included in the sputteringprocess in a one-second cycle and equally long on the average over time.After the predetermined layer thickness of the titanium aluminum nitridelayer being deposited here has been reached, the process gas is removedand replaced with an argon-oxygen mixture. The switching device nowconnects the two aluminum targets 38″ and 38′″ to the output terminalsof the power supply device 40 and aluminum oxide is deposited. When thealuminum oxide layer has reached its predetermined thickness, thedeposition of the layer system is concluded.

The coating device is surrounded by a system of screen plates 41, whichis potential-free. Parts 42 of these screen plates 41 protrude into thespace between the targets 38, 38′, 38″, and 38′″ and the tube 35 as thesubstrate. Because of their geometric form and the resulting electricalfield, they contribute to a further increase of the average plasmadensity in the substrate region. The device described is appropriate fordepositing a layer system with the highest degree of quality because thelayer formation takes place under intensive plasma activation.

Naturally, the invention is not limited to the exemplary embodimentsdescribed. Thus, it is easily possible to change the arrangement of thesubstrates and the targets relative to one another to a large extent.The number of targets and the respective common switching especially canbe changed dramatically. The latter is especially advantageous forproducing specific layer systems on the substrates. In the same sense,several bipolar power supply devices and switching devices, each ofwhich acts together with a part of the targets, can also beadvantageous.

What is claimed is:
 1. A process for coating substrates utilizingbipolar pulsed magnetron sputtering in the frequency range between 10kHz and 100 kHz in a device which includes at least three targets, theprocess comprising: connecting at least two targets at a time to apotential-free bipolar power supply device; sputtering the at least twotargets in a bipolar manner for a predetermined period of time; changingthe connecting of the at least two targets to the bipolar power supplydevice according to a technologically predetermined program; arrangingthe at least two targets relative to the substrates in a manner suchthat during each reversing discharge, the substrates are located atleast partially inside a discharge current between the targets which areactive at the time; creating a region of high plasma density; locatingthe substrates essentially in the region of high plasma density; andcoating the substrates in the region of high plasma density.
 2. Theprocess of claim 1, wherein the changing occurs one of temporallyperiodically and aperiodically.
 3. The process of claim 1, wherein thepredetermined period of time comprises at least 10 polarity reversals ofa bipolar magnetron discharge.
 4. The process of claim 3, wherein thepredetermined period of time comprises between 1,000 and 100,000polarity reversals.
 5. The process of claim 1, wherein at least one of amaterial of the targets and the technologically predetermined program isadapted to a desired layer deposition.
 6. The process of claim 1,wherein at least one of a material of the targets and thetechnologically predetermined program is adapted to a desired coatingtask.
 7. The device of claim 1, wherein the substrates comprise at leastone of an optical, an electrical, and a mechanical component or tool. 8.A device for coating substrates utilizing bipolar pulsed magnetronsputtering in the frequency range between 10 and 100 kHz, the devicecomprising: at least three magnetron sources; each of the at least threemagnetron sources comprising a target; at least two of the targets beingconnected at a time to a potential-free bipolar power supply device; theat least three targets being arranged relative to the substrates in sucha way that the substrates are located at least partially inside adischarge current during a coating of the substrates; a switching deviceadapted to connect the targets to the bipolar power supply device; and atechnological predetermined program for controlling the switchingdevice, wherein the switching device connects at least two of thetargets at a time to the bipolar power supply device according to thetechnologically predetermined program, wherein a region of high plasmadensity is created by the targets, wherein the substrates are locatedessentially in the region of high plasma density, and wherein thesubstrates are coated in the region of high plasma density.
 9. Thedevice of claim 8, wherein the at least three targets comprise at leastfour targets.
 10. The device of claim 9, wherein at least two of the atleast four targets are arranged on one side of the substrates andwherein at least two of the at least four targets are arranged onanother side of the substrates.
 11. The device of claim 8, wherein theat least three targets are arranged to surround the substrates.
 12. Thedevice of claim 8, wherein at least one of the at least three targetsand the substrates are adapted to be movable.
 13. The device of claim 8,wherein the at least three targets comprise four targets, wherein two ofthe four targets are arranged on opposite sides of the substrates, andwherein one of the two targets on each side of the substrates is adaptedto be simultaneously connected to the bipolar power supply device. 14.The device of claim 8, wherein at least one of the at least threetargets, which is arranged on one side of the substrates, is constantlyconnected to the bipolar power supply device and wherein at least two ofthe at least three targets, which are arranged on another side of thesubstrates, are changeably connected to the switching device.
 15. Thedevice of claim 8, wherein the at least three magnetron sources arespaced aparat such that their corresponding magnetic fields do notsignificantly influence one another.
 16. The device of claim 8, furthercomprising a device arranged to surround the at least three magnetrons.17. The device of claim 16, wherein the device arranged to surround theat least three magnetrons comprises one of a grounded screen andpotential-free screen.
 18. The device of claim 16, wherein the devicearranged to surround the at least three magnetrons protrudes into anopen area between a target plane and the substrates.
 19. The device ofclaim 8, wherein the substrates comprise at least one of an optical, anelectrical, and a mechanical component or tool, and wherein device isadapted to produce one of more decorative of functional layers on thesubstrates.
 20. A device for coating substrates utilizing bipolar pulsedmagnetron sputtering in the frequency range between 10 and 100 kHz, thedevice comprising: at least three magnetron sources; each of the atleast three magnetron sources comprising a target; at least two of thetargets being connected to a potential-free bipolar power supply device;the at least three targets being arranged relative to the substrates insuch a way that the substrates are located at least partially inside adischarge current during a coating of the substrates; a switching deviceadapted to connect the targets to the bipolar power supply device; and atechnological predetermined program for controlling the switchingdevice, wherein the switching device connects at least two of thetargets at a time to the bipolar power supply device according to thetechnologically predetermined program, wherein at least one of the atleast three targets comprises a central target which is centrallydisposed and at least two of the at least three targets compriseperipheral targets which are peripherally arranged, whereby thesubstrates are disposed between the central target and the peripheraltargets.
 21. The device of claim 20, wherein the central targetcomprises at least one of tube-shaped, connected to the bipolar powersupply device, and a central rotatable magnet arrangement.
 22. Thedevice of claim 20, wherein the central target is rotatable.
 23. Adevice for coating substrates utilizing bipolar pulsed magnetronsputtering in the frequency range between 10 and 100 kHz, the devicecomprising: a bipolar power supply; a switching device coupled to thebipolar power supply; a program adapted to control the switching device;at least three magnetron sources; at least two of the at least threemagnetron sources being coupled to the switching device; at least one ofthe at least three magnetron sources being coupled to one of theswitching device and the bipolar power supply; each of the at leastthree magnetron sources comprising a target; wherein the switchingdevice connects at least two of the targets at a time to the bipolarpower supply according to the program, wherein a region of high plasmadensity is created by the targets, wherein the substrates are locatedessentially in the region of high plasma density, and wherein thesubstrates are coated in the region of high plasma density.